swc-project/swc

SWC primarily extends through typed passes, visitor traits, feature-gated modules, and binding adapters. Plugins have a configurable sequence and an injectable execution runtime rather than a single permanently fixed backend. CLI operations follow a command enum and execution trait. Generated visitors and release carrier formats introduce additional maintenance contracts that extensions must preserve.

• Compiler::process_js_with_custom_pass accepts factories for before/after Pass implementations; its documented before-pass position follows decorators, resolver, and TypeScript stripping, and the after pass is appended to the built pass.
  crates/swc/src/lib.rs#L938-965crates/swc/src/lib.rs#L986-988
• Visit provides per-node traversal hooks, and overriding a method requires explicit child recursion; the generated visitor file directs maintainers to tools/generate-code rather than manual edits.
  crates/swc_ecma_visit/src/generated.rs#L1-20tools/generate-code/src/main.rs#L25-35tools/generate-code/src/main.rs#L57-64
• JscExperimental.plugins stores ordered PluginConfig module-name/JSON-option pairs; plugin_env_vars and cache_root configure host inputs, and run_plugin_first moves plugin execution ahead of built-in transforms.
  crates/swc/src/plugin.rs#L47-67crates/swc/src/config/mod.rs#L1520-1544crates/swc/src/config/mod.rs#L945-963
• RuntimeOptions::plugin_runtime accepts Arc<dyn Runtime>; Runtime implementers supply identifier, module preparation, initialization, and optional cache operations, with Wasmer chosen by the corresponding default feature.
  crates/swc/src/config/mod.rs#L205-228crates/swc_plugin_runner/src/runtime.rs#L26-73
• ModuleConfig is a tagged enum whose build function constructs module transformation passes; adding a format requires accounting for both the feature-enabled enum and the deserialization-only stub.
  crates/swc/src/config/mod.rs#L1600-1635crates/swc/src/config/mod.rs#L1640-1694
• Bundler inputs are replaceable through Load, returning SourceFile, Module, and Helpers; Resolve is separately re-exported, allowing loading and module resolution to evolve independently.
  crates/swc_bundler/src/load.rs#L6-43crates/swc_bundler/src/resolve.rs#L1-1bindings/binding_core_node/src/bundle.rs#L34-38
• CLI extensions plug into the Clap Command enum, implement CommandRunner::execute, and add dispatch in run; repository maintenance tasks use a separate xtask enum for Es, Bench, Git, Npm, and Clean.
  crates/swc_cli_impl/src/commands/mod.rs#L15-37crates/swc_cli_impl/src/lib.rs#L7-16xtask/src/main.rs#L20-37
• Legacy JavaScript Plugin callbacks remain composable through plugins(ps) but are deprecated in favor of WASM; native and wasm32/plugin-disabled builds have different plugin availability branches, including warning-and-skip behavior.
  packages/core/src/index.ts#L133-143packages/core/src/index.ts#L304-335crates/swc/src/config/mod.rs#L849-900